text: . Troponin I (yellow) is no longer bound to actin. Troponin T (blue) anchors the complex on tropomyosin -->In both cardiac and skeletal muscles, muscular force production is controlled primarily by changes in the intracellular calcium concentration. In general, when calcium rises, the muscles contract and, when calcium falls, the muscles relax. Troponin, along with actin and tropomyosin, is the protein complex to which calcium binds to trigger the production of muscular force.